This is a continuation-in-part of my copending application, Ser. No. 844,924 filed Oct. 25, 1977.
This invention relates to a solar energy collecting means, and more particularly to a collector which utilizes the principles of heat conduction to a heat transfer pipe connected to the collection-absorption part of the collector.
In the preferred embodiment, an absorption means having a plurality of generally vertical planar sides is disposed between two reflective surfaces in order to absorb reflected or reflected-concentrated solar rays.
Use of a central absorbing member in combination with parabolic reflecting surfaces is taught in U.S. Pat. Nos. 4,024,852, 4,038,964 and 3,321,012. These patents describe central planar absorbers having either a fluid tubular member arranged circuituously inside a central opening (U.S. Pat. No. 4,038,964) or a plurality of fluid conduits inside the central opening (U.S. Pat. No. 4,024,852).
U.S. Pat. No. 3,321,012 shows the advantageous use of a similar planar absorber, but uses a central cavity in the absorber as a fluid passage in combination with curvilinear reflective surfaces on each side of the absorber.
In all three patents referenced above, the absorber itself becomes, or contains therein, one or more fluid passages that surround the heat transfer medium.
In the instant invention, the solar ray absorber means can be a thin metallic strip or a metallic piece of greater cross sectional area, but in either case, the absorption coated solar ray absorber is monolithic and does not have fluid conduits therein. In this invention, the lower edge of the absorber is connected with a fluid conveying member that is mounted in butting relationship and therefore adjacent to and below the major portion of the "effective" absorption area. In another embodiment, the fluid conveying member can be mounted above the major portion of the "effective" absorption area, or there can be a fluid converging member at each end of the absorber.
Construction according to the present invention has distinct advantages over prior art teachings, for example, the present invention can utilize a very small diameter tubular member below the single planar absorber. The primary benefit of using a monolithic planar member resides in the fact that commercially available strip stock or thin bar stock can be used for solar ray absorption without further processing except for coating and connecting it to the heat transfer tube. Placement of the planar absorber centrally of the adjacent reflective surfaces maximizes the incidence of impinging solar rays over a wide spectrum of daily solar angles.
It is noted that the absorber length of the present invention is most effective when its length equals the axial length of the reflective surface, thereby defining the best possible cost relationship between reflectors and absorbers. The beneficial geometric relationship of a thin rectangular strip or bar minimizes deflection of the absorber and has sufficient bend resistance to support small diameter tubing since the absorber and tubing will be operatively connected along an edge portion of the planar absorber member.
While the preferred embodiment shows the tubular heat transfer pipe connected to the bottom edge of the planar absorber, it is within the scope of this invention that the fluid carrying pipe can be positioned above the planar absorber and connected thereto at the upper edge without any measureable difference in the concentration ratio as opposed to location at the bottom edge of the absorber. When placed at the top of the absorber, the fluid carrying pipe can be positioned above the zenith of the reflector surfaces thereby minimizing any re-reflection of rays from the external periphery of the pipe which condition would occur whenever a true parabolic reflector surface is not used. A pipe connected to the absorber plate along a top edge that is slightly above the zenith of the reflector surfaces would be the most effective construction for use with any non-parabolic surface.
If two pipes are used, two separate fluids may be utilized and independently heated.
Another advantage of using small diameter tubular fluid carrying pipes is the reduction in circumferential area that must be sealed to prevent fluid leakage where the pipes are inserted into manifold members.
According to U.S. Pat. No. 3,321,012, fluid carrying tubes with a central flattened portion could be used as absorbers, however, in order to define an absorber that is effective from the nadir to the zenith of the reflector surfaces, a much larger diameter tube must be used with the resultant disadvantage that a significant length is involved in transition from the flattened to the circular cross section.
In another embodiment of the present invention, the substantially planar absorber can be rotated about the heat transfer pipe, said transfer pipe being fixedly and non-rotatably secured to the end manifolds, this arrangement minimizing reflection of rays uselessly into space, particularly when the solar angle is low.
In another embodiment, an evacuated oblongated transparent encasement can enclose the coacting absorber-heat transfer pipe.